JP2008238048A - Precision filter unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a precision filter unit using a porous alumina membrane filter with excellent pressure resistance and an improved filtration flow rate. <P>SOLUTION: The precision filter unit is provided at least with: the porous alumina membrane filter composed of an anode oxide film of aluminum and provided with micropores in which a regularization degree is ≥50% and the standard deviation of a pore diameter is within 10% of an average pore diameter; and a porous material to be brought into contact with the surface on one side at least of the porous alumina membrane filter, in which the average pore diameter is 500 nm to 10 mm, an opening area per unit area is wider than the opening area per unit area of the porous alumina membrane filter, and Young's modulus is larger than 660 MPa. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a precision filter unit.

  Organic membrane filters and inorganic membrane filters are known as membrane filters in practical use in the field of microfiltration.

  Many organic membrane filters do not have independent pores and have a relatively wide pore size distribution, so that the most important functions of the filter are specific substances (for example, CMP slurry particles; resist pigments and dyes; IJ In order to improve the separation accuracy of ink, magnetic material, cells (cell culture insert use, etc.), molecules having a size fraction such as fullerene, solvents such as DMSO, etc., various researches are being conducted.

For example, Non-Patent Document 1 discloses so-called track etching in which an organic film made of a polymer is irradiated with high-energy particles generated from a nuclear reactor, and the tracks through which the particles have passed through the organic film are etched to form pores. A scheme has been proposed.
However, this track etching method can obtain independent narrow pores with a narrow pore size distribution perpendicular to the organic film, but in order to avoid the generation of double holes due to the incidence of particles overlapping during track formation, There was a problem that the pore density, so-called porosity, could not be increased.

On the other hand, a porous alumina membrane filter using an anodic oxide film of aluminum is known as an inorganic membrane filter without such problems (for example, see Non-Patent Document 2).
This porous alumina membrane filter is made by anodizing aluminum in an acidic electrolyte so that independent pores with a narrow pore size distribution are arranged with a high porosity, so the filtration flow rate per hour is high, Moreover, it can be manufactured at low cost.

However, the porous alumina membrane filter itself is an aluminum anodized film, so that the film itself has high hardness but is brittle to the bending force. For example, in a filtration process under high pressure conditions, There is a problem that the device itself is damaged.
Therefore, for example, as described in Patent Document 1 and the like, a method of fixing the filter material main body with a cartridge has been proposed, but this method cannot sufficiently prevent breakage, and further improvement is possible. It is desired.

T.A. D. Block, Membrane Filtration, Sci. Tech, Inc. , Madison (1983) Hideki Masuda, “New Technology of Porous Membrane Using Anodization”, Altopia, July 1995 Special table 2004-512155 gazette

  Accordingly, an object of the present invention is to provide a precision filter unit using a porous alumina membrane filter having excellent pressure resistance and improved filtration flow rate.

  As a result of intensive studies to achieve the above object, the present inventor has used a predetermined porous alumina membrane filter made of an anodized aluminum film and a porous material having a specific relationship with the porous alumina membrane filter. It was found that the pressure resistance was excellent and the filtration flow rate was improved, and the present invention was completed.

That is, the present invention provides the following (i) to (v).
(I) Porous having a micropore comprising an anodic oxide film of aluminum and having a degree of ordering defined by the following formula (1) of 50% or more and a standard deviation of the pore diameter within 10% of the average pore diameter. An alumina membrane filter,
A porous material in contact with the surface of at least one side of the porous alumina membrane filter, having an average pore diameter of 500 nm to 10 mm, and an opening area per unit area (hereinafter also referred to as “aperture ratio”). A porous material having a larger Young's modulus than 660 MPa, which is larger than the aperture area per unit area of the alumina membrane filter;
A precision filter unit comprising at least
Ordering degree (%) = B / A × 100 (1)
In the above formula (1), A represents the total number of micropores in the measurement range. B is centered on the center of gravity of one micropore, and when a circle with the shortest radius inscribed in the edge of another micropore is drawn, the center of gravity of the micropore other than the one micropore is placed inside the circle. This represents the number in the measurement range of the one micropore to be included.

  (Ii) The precision filter unit according to (i), wherein the porous material is in contact with the surfaces on both sides of the porous alumina membrane filter.

(Iii) The porous alumina membrane filter is at least
Anodizing to form an oxide film having micropores by anodizing an aluminum substrate;
A separation treatment for removing the aluminum substrate after the anodizing treatment and separating the oxide film from the aluminum substrate;
A penetration treatment for penetrating the micropores of the oxide film separated by the separation treatment;
The precision filter unit according to (i) or (ii), which is formed by applying the components in this order.

(Iv) The precision filter unit according to the above (iii), wherein a heat treatment is performed to heat the oxide film formed by the anodizing treatment at a temperature of 50 ° C. or higher for at least 10 minutes before the separation treatment.
(V) The precision filter unit according to (iii) or (iv), wherein a protective treatment for forming a protective film that prevents hydration is formed on the surface of the oxide film after the penetration treatment.

As will be described below, according to the present invention, it is possible to provide a precision filter unit using a porous alumina membrane filter having excellent pressure resistance and improved filtration flow rate.
The precision filter unit of the present invention is very useful because it can improve the filtration flow rate because the filter itself does not break even during filtration under high pressure conditions.

The present invention is described in detail below.
The precision filter unit of the present invention is made of an anodized aluminum film, the degree of ordering defined by the above formula (1) is 50% or more, and the standard deviation of the pore diameter is within 10% of the average pore diameter. A porous alumina membrane filter having micropores;
A porous material in contact with the surface of at least one side of the porous alumina membrane filter, the average pore diameter is 500 nm to 10 mm, the porosity is higher than the porosity of the porous alumina membrane filter, and the Young's modulus is It is a precision filter unit comprising at least a porous material larger than 660 MPa.
Next, the porous alumina membrane filter and the porous material used in the precision filter unit of the present invention will be described in detail.

[Porous alumina membrane filter]
The porous alumina membrane filter constituting the precision filter unit of the present invention is composed of an anodized aluminum film, the degree of ordering defined by the following formula (1) is 50% or more, and the standard deviation of the pore diameter is an average. It has micropores that are within 10% of the pore diameter.

  Ordering degree (%) = B / A × 100 (1)

  In the above formula (1), A represents the total number of micropores in the measurement range. B is centered on the center of gravity of one micropore, and when a circle with the shortest radius inscribed in the edge of another micropore is drawn, the center of gravity of the micropore other than the one micropore is placed inside the circle. This represents the number in the measurement range of the one micropore to be included.

Here, FIG. 1 is an explanatory diagram of a method for calculating the degree of ordering of pores. The above formula (1) will be described more specifically with reference to FIG.
The micropore 1 shown in FIG. 1 (A) draws a circle 3 (inscribed in the micropore 2) having the shortest radius that is centered on the center of gravity of the micropore 1 and inscribed in the edge of another micropore. In this case, the center of the circle 3 includes six centroids of micropores other than the micropore 1. Therefore, the micropore 1 is included in B.
The micropore 4 shown in FIG. 1 (B) draws a circle 6 (inscribed in the micropore 5) having the shortest radius that is centered on the center of gravity of the micropore 4 and inscribed in the edge of another micropore. In this case, the center of gravity of the micropores other than the micropores 4 is included inside the circle 6. Therefore, the micropore 4 is not included in B.
Further, the micropore 7 shown in FIG. 1B is centered on the center of gravity of the micropore 7 and has the shortest radius 9 inscribed in the edge of another micropore (inscribed in the micropore 8). Is drawn, the circle 9 includes seven centroids of micropores other than the micropore 7. Therefore, the micropore 7 is not included in B.

On the other hand, in the present invention, the average pore diameter (average pore diameter) and the standard deviation of the pore diameter (pore diameter) of the micropore are obtained by photographing a surface photograph (magnification 20000 times) with an FE-SEM and present in a 1 μm × 1 μm visual field. It is the value calculated | required by the following formula about the micropore to do.

In the present invention, by using a porous alumina membrane filter having micropores with a degree of ordering of 50% or more, the resulting precision filter unit of the present invention has excellent pressure resistance during filtration.
The degree of ordering is preferably 60% or more, and more preferably 80% or more.

Moreover, in this invention, the filtration flow volume of the precision filter unit of this invention obtained by using the porous alumina membrane filter which has a micropore whose pore diameter standard deviation is less than 10% of an average pore diameter improves.
Further, the standard deviation of the pore diameter is preferably within 7%, and more preferably within 5%.

The method for producing such a porous alumina membrane filter is not particularly limited, but at least anodization treatment (hereinafter also referred to as “anodization treatment (A)”) in which an aluminum substrate is anodized to form an oxide film having micropores. ), And after the anodizing treatment, the aluminum substrate is removed and the oxide film is separated from the aluminum substrate (hereinafter also referred to as “separation treatment (C)”), and the oxidation separated by the separation treatment. It is preferably formed by performing a penetration process (hereinafter also referred to as “penetration process (D)”) that penetrates the micropores of the film in this order.
In addition, before the separation treatment, a heat treatment (hereinafter also referred to as “heat treatment (B)”) is performed in which the oxide film formed by the anodization treatment is heated at a temperature of 50 ° C. or higher for at least 10 minutes. More preferred.
Further, it is more preferable to perform a protective treatment (hereinafter also referred to as “protective treatment (E)”) for forming a protective film that prevents hydration on the surface of the oxide film after the penetration treatment.
Below, an aluminum substrate and each process are explained in full detail.

[Aluminum substrate]
The aluminum substrate is not particularly limited, and specific examples thereof include a pure aluminum plate; an alloy plate containing aluminum as a main component and containing a trace amount of foreign elements; and depositing high-purity aluminum on low-purity aluminum (for example, recycled material). Examples of the substrate include: a substrate in which high purity aluminum is coated on the surface of a silicon wafer, quartz, glass or the like by a method such as vapor deposition or sputtering; a resin substrate in which aluminum is laminated;

  In the present invention, of the aluminum substrate, the surface to be anodized, which will be described later, preferably has an aluminum purity of 99.5% by mass or more, more preferably 99.9% by mass or more, 99 More preferably, it is at least 99 mass%. When the aluminum purity is in the above range, the regularity of the pore arrangement of the micropores is sufficient.

  In the present invention, the surface of the aluminum substrate to be subjected to anodization described later is preferably subjected to degreasing and mirror finishing in advance, particularly from the viewpoint of improving the regularity of the pore arrangement, Heat treatment is preferably performed.

<Heat treatment>
When heat treatment is performed, it is preferably performed at 200 to 350 ° C. for about 30 seconds to 2 minutes. Specifically, for example, a method of placing an aluminum substrate in a heating oven can be used.
By performing such heat treatment, the regularity of the arrangement of micropores generated by an anodic oxidation process described later is improved.
Moreover, it is preferable to cool the aluminum substrate after heat treatment rapidly. As a method for cooling, for example, a method of directly putting it into water or the like can be mentioned.

<Degreasing treatment>
The degreasing treatment uses acid, alkali, organic solvent, etc. to dissolve and remove the organic components such as dust, fat, and resin adhered to the surface of the aluminum substrate, and in each treatment described later due to the organic components. This is done for the purpose of preventing the occurrence of defects.

Specifically, as the degreasing treatment, for example, a method in which an organic solvent such as various alcohols (for example, methanol), various ketones (for example, methyl ethyl ketone), benzine, volatile oil or the like is brought into contact with the aluminum substrate surface at room temperature (organic Solvent method); a method of bringing a liquid containing a surfactant such as soap or neutral detergent into contact with the aluminum substrate surface at a temperature from room temperature to 80 ° C., and then washing with water (surfactant method); concentration of 10 to 200 g A method in which an aqueous solution of sulfuric acid / L is brought into contact with the aluminum substrate surface at a temperature from room temperature to 70 ° C. for 30 to 80 seconds and then washed with water; while contacting about seconds, the aluminum substrate surface and the electrolyte by passing a direct current of a current density of 1 to 10 a / dm ² in the cathode, the , A method of neutralizing by bringing a nitric acid aqueous solution having a concentration of 100 to 500 g / L into contact; while bringing various known anodizing electrolytes into contact with the aluminum substrate surface at room temperature, the aluminum substrate surface is used as a cathode and a current density of 1 to A method in which a 10 A / dm ² direct current is applied or an alternating current is applied for electrolysis; an alkaline aqueous solution having a concentration of 10 to 200 g / L is brought into contact with the aluminum substrate surface at 40 to 50 ° C. for 15 to 60 seconds; A method of neutralizing by bringing a nitric acid aqueous solution having a concentration of 100 to 500 g / L into contact; an emulsion obtained by mixing light oil, kerosene, etc. with a surfactant, water, etc. is brought into contact with the aluminum substrate surface at a temperature from room temperature to 50 ° C. Then, a method of washing with water (emulsification and degreasing method); a mixed solution of sodium carbonate, phosphates, surfactant, etc. on the surface of the aluminum substrate at a temperature from room temperature to 50 ° Contacting 0-180 seconds, then, a method of washing with water (phosphate method); and the like.

  Among these, the organic solvent method, the surfactant method, the emulsion degreasing method, and the phosphate method are preferable from the viewpoint that the fat content on the aluminum surface can be removed while the aluminum hardly dissolves.

  Moreover, a conventionally well-known degreasing agent can be used for a degreasing process. Specifically, for example, various commercially available degreasing agents can be used by a predetermined method.

<Mirror finish processing>
The mirror finishing process is performed in order to eliminate unevenness on the surface of the aluminum substrate, for example, rolling streaks generated during the rolling of the aluminum substrate, and improve the uniformity and reproducibility of the sealing process by an electrodeposition method or the like.
In the present invention, the mirror finish is not particularly limited, and a conventionally known method can be used. Examples thereof include mechanical polishing, chemical polishing, and electrolytic polishing.

  Examples of the mechanical polishing include a method of polishing with various commercially available polishing cloths, a method of combining various commercially available abrasives (for example, diamond, alumina) and a buff. Specifically, when an abrasive is used, a method in which the abrasive used is changed from coarse particles to fine particles over time is preferably exemplified. In this case, the final polishing agent is preferably # 1500. Thereby, the glossiness can be 50% or more (in the case of rolled aluminum, both the rolling direction and the width direction are 50% or more).

As chemical polishing, for example, “Aluminum Handbook”, 6th edition, edited by Japan Aluminum Association, 2001, p. Examples thereof include various methods described in 164 to 165.
Further, phosphoric acid - nitric acid method, Alupol I method, Alupol V method, Alcoa R5 _{method, H 3 PO 4 -CH 3 COOH} -Cu _{method, H 3 PO 4 -HNO 3 -CH} 3 COOH method are preferable. Of these, the phosphoric acid-nitric acid method, the H ₃ PO ₄ —CH ₃ COOH—Cu method, and the H ₃ PO ₄ —HNO ₃ —CH ₃ COOH method are preferable.
By chemical polishing, the glossiness can be made 70% or more (in the case of rolled aluminum, both the rolling direction and the width direction are 70% or more).

As electrolytic polishing, for example, “Aluminum Handbook”, 6th edition, edited by Japan Aluminum Association, 2001, p. 164-165; various methods described in US Pat. No. 2,708,655; “Practical Surface Technology”, vol. 33, no. 3, 1986, p. The method described in 32-38;
By electropolishing, the gloss can be 70% or more (in the case of rolled aluminum, both the rolling direction and the width direction are 70% or more).

  These methods can be used in appropriate combination. Specifically, for example, a method of performing mechanical polishing in which the abrasive is changed from coarse particles to fine particles with time, and then performing electrolytic polishing is preferable.

By mirror finishing, for example, a surface having an average surface roughness R _{a of} 0.1 μm or less and a glossiness of 50% or more can be obtained. The average surface roughness _Ra is preferably 0.03 μm or less, and more preferably 0.02 μm or less. Further, the glossiness is preferably 70% or more, and more preferably 80% or more.
The glossiness is a regular reflectance obtained in accordance with JIS Z8741-1997 “Method 3 60 ° Specular Gloss” in the direction perpendicular to the rolling direction. Specifically, using a variable angle gloss meter (for example, VG-1D, manufactured by Nippon Denshoku Industries Co., Ltd.), when the regular reflectance is 70% or less, the incident reflection angle is 60 degrees and the regular reflectance is 70%. In the case of exceeding, the incident / reflection angle is 20 degrees.

[Anodic oxidation treatment (A)]
The anodizing treatment (A) is a treatment for forming an oxide film having micropores on the surface of the aluminum substrate by anodizing the aluminum substrate.
As the anodizing treatment, a conventionally known method can be used. Specifically, it is preferable to use the self-ordering method described later.

The self-ordering method is a method of improving the regularity by utilizing the property that the micropores of the anodized film are regularly arranged and removing the factors that disturb the regular arrangement. Specifically, high-purity aluminum is used, and an anodized film is formed at a low speed over a long period of time (for example, several hours to several tens of hours) at a voltage according to the type of the electrolytic solution.
In this method, since the pore diameter depends on the voltage, a desired pore diameter can be obtained to some extent by controlling the voltage.

  In order to form micropores by the self-ordering method, anodizing treatment (a-1) described later may be performed, but preferably anodizing treatment (a-1) described later, film removal treatment (a- It is preferable to form by the method of implementing 2) and re-anodizing treatment (a-3) in this order.

<Anodizing treatment (a-1)>
The average flow rate during the anodizing treatment is preferably 0.5 to 20.0 m / min, more preferably 1.0 to 15.0 m / min, and 2.0 to 10.0 m / min. More preferably, it is min. By performing anodizing treatment at a flow rate in the above range, uniform and high regularity can be obtained.
Moreover, the method of flowing the electrolytic solution under the above-mentioned conditions is not particularly limited, but, for example, a method using a general stirring device such as a stirrer is used. In particular, it is preferable to use a stirrer that can control the stirring speed with a digital display because the average flow rate can be controlled. Examples of such a stirring apparatus include “Magnetic Stirrer HS-50D (manufactured by AS ONE)” and the like.

For the anodizing treatment (a-1), for example, a method of energizing an aluminum substrate as an anode in a solution having an acid concentration of 0.01 to 5 mol / L can be used.
The solution used for the anodizing treatment (a-1) is preferably an acid solution, and sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, amidosulfonic acid, glycolic acid, tartaric acid, Malic acid, citric acid, and the like are more preferable, and sulfuric acid, phosphoric acid, and oxalic acid are particularly preferable. These acids can be used alone or in combination of two or more.

The conditions for the anodizing treatment (a-1) vary depending on the electrolyte used, and thus cannot be determined unconditionally. In general, however, the electrolyte concentration is 0.01 to 5 mol / L, and the solution temperature is -10 to 10. It is preferably 30 ° C., current density 0.01 to 20 A / dm ² , voltage 3 to 300 V, electrolysis time 0.5 to 30 hours, electrolyte concentration 0.05 to 3 mol / L, liquid temperature −5 to 25 It is more preferable that it is C, current density 0.05-15A / dm < ² >, voltage 5-250V, electrolysis time 1-25 hours, electrolyte concentration 0.1-1 mol / L, liquid temperature 0-20 degreeC, current More preferably, the density is 0.1 to 10 A / dm ² , the voltage is 10 to 200 V, and the electrolysis time is 2 to 20 hours.

  The treatment time for the anodizing treatment (a-1) is preferably 0.5 minutes to 16 hours, more preferably 1 minute to 12 hours, and even more preferably 2 minutes to 8 hours.

  The anodizing treatment (a-1) can be performed under a constant voltage, or a method of changing the voltage intermittently or continuously. In this case, it is preferable to decrease the voltage sequentially. This makes it possible to reduce the resistance of the anodized film, and fine micropores are formed in the anodized film, which is preferable in terms of improving uniformity, particularly when sealing treatment is performed by electrodeposition. .

  In the present invention, the thickness of the anodized film formed by such anodizing treatment (a-1) is preferably 0.1 to 2000 μm, more preferably 1 to 1000 μm. More preferably, it is -500 micrometers.

In the present invention, the pore diameter of the micropore formed by such anodizing treatment (a-1) is preferably 0.01 to 0.5 μm.
The average pore density of the micropores is preferably 50 to 1500 / μm ² .
Further, the area ratio occupied by the micropores is preferably 20 to 50%.
Here, the area ratio occupied by the micropores is defined by the ratio of the total area of the openings of the micropores to the area of the aluminum surface.

<Film removal treatment (a-2)>
The film removal process (a-2) is a process for dissolving and removing the anodized film formed on the surface of the aluminum substrate by the anodizing process (a-1).
After forming the anodized film on the surface of the aluminum substrate by the anodizing treatment (a-1), the heat treatment (B) or the separation treatment (C) described later may be performed immediately, but the anodizing treatment (a- After 1), a film removal process (a-2) and a re-anodizing process (a-3) to be described later are performed in this order, and then a heating process (B) or a separation process (C) to be described later is performed. Is preferred.

  Since the anodic oxide film has higher regularity as it gets closer to the aluminum substrate, the anodic oxide film once removed by this film removal treatment (a-2) and remaining on the surface of the aluminum substrate. The bottom portion can be exposed on the surface to obtain regular depressions. Therefore, in the film removal treatment (a-2), aluminum is not dissolved, but only the anodized film made of alumina (aluminum oxide) is dissolved.

  Alumina solution includes chromium compound, nitric acid, phosphoric acid, zirconium compound, titanium compound, lithium salt, cerium salt, magnesium salt, sodium fluorosilicate, zinc fluoride, manganese compound, molybdenum compound, magnesium compound, barium compound and An aqueous solution containing at least one selected from the group consisting of simple halogens is preferred.

Specific examples of the chromium compound include chromium (III) oxide and anhydrous chromium (VI) acid.
Examples of the zirconium-based compound include zircon ammonium fluoride, zirconium fluoride, and zirconium chloride.
Examples of the titanium compound include titanium oxide and titanium sulfide.
Examples of the lithium salt include lithium fluoride and lithium chloride.
Examples of the cerium salt include cerium fluoride and cerium chloride.
Examples of the magnesium salt include magnesium sulfide.
Examples of the manganese compound include sodium permanganate and calcium permanganate.
Examples of the molybdenum compound include sodium molybdate.
Examples of magnesium compounds include magnesium fluoride pentahydrate.
Examples of barium compounds include barium oxide, barium acetate, barium carbonate, barium chlorate, barium chloride, barium fluoride, barium iodide, barium lactate, barium oxalate, barium perchlorate, barium selenate, selenite. Examples thereof include barium, barium stearate, barium sulfite, barium titanate, barium hydroxide, barium nitrate, and hydrates thereof. Among the barium compounds, barium oxide, barium acetate, and barium carbonate are preferable, and barium oxide is particularly preferable.
Examples of halogen alone include chlorine, fluorine, and bromine.

Among them, the alumina solution is preferably an aqueous solution containing an acid. Examples of the acid include sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, and the like, and a mixture of two or more acids may be used.
The acid concentration is preferably 0.01 mol / L or more, more preferably 0.05 mol / L or more, and still more preferably 0.1 mol / L or more. There is no particular upper limit, but generally it is preferably 10 mol / L or less, more preferably 5 mol / L or less. An unnecessarily high concentration is not economical, and if it is higher, the aluminum substrate may be dissolved.

  The alumina solution is preferably −10 ° C. or higher, more preferably −5 ° C. or higher, and still more preferably 0 ° C. or higher. In addition, since the starting point of ordering will be destroyed and disturbed if it processes using the boiling alumina solution, it is preferable to use it without boiling.

  The alumina solution dissolves alumina and does not dissolve aluminum. Here, the alumina solution may not dissolve aluminum substantially or may dissolve it slightly.

  The film removal treatment (a-2) is performed by bringing the aluminum substrate on which the anodized film is formed into contact with the above-described alumina solution. The method of making it contact is not specifically limited, For example, the immersion method and the spray method are mentioned. Of these, the dipping method is preferred.

The dipping method is a treatment in which an aluminum substrate on which an anodized film is formed is dipped in the above-described alumina solution. Stirring during the dipping process is preferable because a uniform process is performed.
The dipping treatment time is preferably 10 minutes or longer, more preferably 1 hour or longer, and further preferably 3 hours or longer and 5 hours or longer.

<Re-anodizing treatment (a-3)>
After removing the anodic oxide film by the film removal treatment (a-2) to form regular depressions on the surface of the aluminum substrate, the degree of ordering of the micropores is higher by performing the anodic oxidation treatment again. An anodized film can be formed.
For the re-anodizing treatment (a-3), a conventionally known method can be used, but it is preferably performed under the same conditions as the above-described anodizing treatment (a-1).
Also, a method of repeatedly turning on and off the current intermittently while keeping the DC voltage constant, and a method of repeatedly turning on and off the current while intermittently changing the DC voltage can be suitably used. According to these methods, fine micropores are generated in the anodic oxide film, which is preferable in that uniformity is improved particularly when sealing treatment is performed by electrodeposition.

When the re-anodizing treatment (a-3) is performed at a low temperature, the arrangement of micropores becomes regular and the pore diameter becomes uniform.
On the other hand, by performing the re-anodizing treatment (a-3) at a relatively high temperature, the arrangement of the micropores can be disturbed, and the variation in pore diameter can be made within a predetermined range. Also, the pore diameter variation can be controlled by the processing time.

  In the present invention, the thickness of the anodized film formed by such re-anodizing treatment (a-3) is preferably 0.1 to 1000 μm, more preferably 1 to 500 μm, More preferably, it is 10-500 micrometers.

In the present invention, the pore diameter of the micropores of the anodized film formed by such anodizing treatment (a-3) is preferably 0.01 to 0.5 μm.
The average pore density is preferably 50-1500 / μm ² .

  In the present invention, instead of the above-described anodic oxidation treatment (a-1) and film removal treatment (a-2), for example, a physical method, a particle beam method, a block copolymer method, a resist pattern / exposure / etching method, etc. Thus, a depression that is a starting point for generating micropores by the re-anodizing treatment (a-3) described above may be formed.

<Physical method>
For example, a method using an imprint method (a transfer method or a press patterning method in which a substrate or a roll having a protrusion is pressed against an aluminum plate to form a recess) can be used. Specifically, a method of forming a depression by pressing a substrate having a plurality of protrusions on the surface thereof against the aluminum surface can be mentioned. For example, a method described in JP-A-10-121292 can be used.
Another example is a method in which polystyrene spheres are arranged in a dense state on the aluminum surface, SiO ₂ is vapor-deposited thereon, then the polystyrene spheres are removed, and the substrate is etched using the vapor-deposited SiO ₂ as a mask to form depressions. It is done.

<Particle beam method>
The particle beam method is a method in which a hollow is formed by irradiating the aluminum surface with a particle beam. The particle beam method has an advantage that the position of the depression can be freely controlled.
Examples of the particle beam include a charged particle beam, a focused ion beam (FIB), and an electron beam.
As the particle beam method, for example, a method described in JP-A-2001-105400 can be used.

<Block copolymer method>
The block copolymer method is a method in which a block copolymer layer is formed on an aluminum surface, a sea-island structure is formed in the block copolymer layer by thermal annealing, and then an island portion is removed to form a depression.
As a block copolymer method, the method described in Unexamined-Japanese-Patent No. 2003-129288 can be used, for example.

<Resist pattern, exposure, etching method>
In the resist pattern / exposure / etching method, the resist on the surface of the aluminum plate is exposed and developed by photolithography or electron beam lithography to form a resist pattern, which is then etched. In this method, a resist is provided and etched to form a recess penetrating to the aluminum surface.

Moreover, in this invention, you may form the oxide film which has a micropore on the aluminum substrate surface by performing the process of following (1)-(4) in this order as said anodizing process (A).
(1) Step of forming an anodic oxide film having micropores on the surface of the aluminum substrate by anodizing the surface of the aluminum substrate (2) Step of partially dissolving the anodic oxide film using acid or alkali (3) A step of growing the micropores in the depth direction by performing anodization treatment (4) A step of removing the anodized film above the inflection point of the cross-sectional shape of the micropores

<Step (1)>
In the step (1), at least one surface of the aluminum substrate is anodized to form an anodized film having micropores on the surface of the aluminum substrate.
Step (1) can be carried out in the same procedure as in the anodizing treatment (a-1).
FIG. 2 is a schematic end view of an aluminum substrate and an anodized film formed on the aluminum substrate for explaining the porous alumina membrane filter used in the present invention.
FIG. 2A shows a state in which the anodic oxide film 14a having the micropores 16a is formed on the surface of the aluminum substrate 12a by the step (1).

<Step (2)>
In step (2), the anodized film formed in step (1) is partially dissolved using acid or alkali.
Here, partially dissolving the anodic oxide film does not completely dissolve the anodic oxide film formed in the step (1), but on the aluminum substrate 12a as shown in FIG. 2B. 2A shows that the surface of the anodic oxide film 14a shown in FIG. 2A and the inside of the micropore 16a are partially dissolved so that the anodic oxide film 14b having the micropores 16b remains.
Further, the dissolution amount of the anodized film is preferably 0.001 to 50% by mass of the whole anodized film, more preferably 0.005 to 30% by mass, and 0.01 to 15% by mass. More preferably. When the dissolution amount is in the above range, the irregular part of the surface of the anodic oxide film can be dissolved to increase the regularity of the micropore array, and the anodic oxide film is formed on the bottom part of the micropore. Thus, the starting point of the anodizing treatment performed in the step (3) can be left.

  Step (2) is performed by bringing the anodized film formed on the aluminum substrate into contact with an acid aqueous solution or an alkali aqueous solution. The method of making it contact is not specifically limited, For example, the immersion method and the spray method are mentioned. Of these, the dipping method is preferred.

When an acid aqueous solution is used in step (2), it is preferable to use an aqueous solution of an inorganic acid such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, or a mixture thereof. Especially, the aqueous solution which does not contain chromic acid is preferable at the point which is excellent in safety | security. The concentration of the acid aqueous solution is preferably 0.01 to 1 mol / L. The temperature of the acid aqueous solution is preferably 25 to 60 ° C.
When an alkaline aqueous solution is used in step (2), it is preferable to use an aqueous solution of at least one alkali selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide. The concentration of the alkaline aqueous solution is preferably 0.01 to 1 mol / L. The temperature of the alkaline aqueous solution is preferably 20 to 35 ° C.
Specifically, for example, 0.5 mol / L, 40 ° C. phosphoric acid aqueous solution, 0.05 mol / L, 30 ° C. sodium hydroxide aqueous solution or 0.05 mol / L, 30 ° C. potassium hydroxide aqueous solution is suitable. Used.
The immersion time in the acid aqueous solution or alkali aqueous solution is preferably 8 to 120 minutes, more preferably 10 to 90 minutes, and still more preferably 15 to 60 minutes.

<Step (3)>
In step (3), the anodization process is again performed on the aluminum substrate in which the anodized film is partially dissolved in step (2) to grow micropores in the depth direction.
As shown in FIG. 2C, the oxidation reaction of the aluminum substrate 12a shown in FIG. 2B proceeds by the anodic oxidation treatment in the step (3), and the aluminum substrate 12b is formed on the aluminum substrate 12b rather than the micropores 16b. An anodic oxide film 14c having micropores 16c grown in the depth direction is formed.

A conventionally known method can be used for the anodizing treatment, but it is preferably performed under the same conditions as the above-described anodizing treatment (a-1).
Also, a method of repeatedly turning on and off the current intermittently while keeping the DC voltage constant, and a method of repeatedly turning on and off the current while intermittently changing the DC voltage can be suitably used. According to these methods, fine micropores are generated in the anodic oxide film, which is preferable in that uniformity is improved particularly when sealing treatment is performed by electrodeposition.
In the above-described method of intermittently changing the voltage, it is preferable to decrease the voltage sequentially. As a result, the resistance of the anodized film can be lowered, and can be made uniform when the electrodeposition treatment is performed later.

  The amount of increase in the thickness of the anodized film is preferably from 0.1 to 100 μm, and more preferably from 0.5 to 50 μm. When the increase amount is in the above range, the regularity of the pore arrangement can be further increased.

<Process (4)>
In step (4), the anodized film above the inflection point 30 in the cross-sectional shape of the micropore 16c shown in FIG. As shown in FIG. 2C, the micropore formed by the self-ordering method has a substantially straight pipe shape except for the upper portion of the micropore 16c. In other words, a portion (a deformed portion) 20 having a cross-sectional shape different from that of the remaining portion of the micropore 16c exists in the upper portion of the micropore 16c. In step (4), the anodized film above the inflection point 30 of the cross-sectional shape of the micropore 16c is removed in order to eliminate such a deformed portion 20 existing on the micropore 16c.
Here, the inflection point 30 refers to a portion where the shape changes remarkably with respect to the main shape (here, substantially straight pipe shape) formed by the cross-sectional shape of the micropore 16c. In the cross-sectional shape of 16c, it refers to a portion where the continuity of the shape is lost with respect to the main shape (substantially straight pipe shape).
By removing the anodic oxide film above the inflection point 30 of the cross-sectional shape of the micropore 16c, the entire micropore 16d has a substantially straight tube shape as shown in FIG.

  In step (4), the inflection point 30 of the cross-sectional shape of the micropore 16c is specified by photographing an FE-SEM of the anodized film 14c after the execution of the step (3) from the cross-sectional direction. The anodic oxide film above may be removed.

However, the deformed portion is generated in the micropore mainly when the anodized film 14a is newly formed on the aluminum substrate 12a as in the step (1). Therefore, in order to remove the anodic oxide film above the inflection point 30 of the cross-sectional shape of the micropore 16c and eliminate the deformed portion 20 above the micropore 16c, the anodic oxide film formed in the step (1) is used. May be removed in step (4).
As will be described later, when the step (3) and the step (4) are repeated twice or more, the deformed portion 30 is eliminated in the anodized film 14d after the step (4) is performed, and the cross-sectional shape of the micropore 16d Since the whole has a substantially straight pipe shape, a new micropore is formed above the micropore formed in step (3) (hereinafter referred to as “step (3 ′)”) following step (4). A deformed part occurs in Therefore, in the step (4) (hereinafter referred to as “step (4 ′)” in this paragraph) to be performed following the step (3 ′), a new upper portion of the micropore formed in the step (3 ′) is added. It is necessary to remove the deformed part. Therefore, in step (4 ′), it is necessary to remove the anodized film above the inflection point of the micropore formed in step (3 ′).

  In the step (4), the process for removing the anodic oxide film above the inflection point of the cross-sectional shape of the micropore 16c may be a polishing process such as mechanical polishing, chemical polishing, and electrolytic polishing. However, as in the step (2), a treatment for dissolving the anodized film using an acid or an alkali is preferable. In this case, as shown in FIG. 2D, an anodic oxide film 14d having a thickness smaller than that of the anodic oxide film 14c shown in FIG.

  In the step (4), when the anodized film is partially dissolved using acid or alkali, the dissolved amount of the anodized film is not particularly limited, and the total amount of the anodized film is not limited. It is preferable that it is 0.01-30 mass%, and it is more preferable that it is 0.1-15 mass%. When the dissolution amount is in the above range, the irregular portion of the surface arrangement of the anodized film can be dissolved, and the regularity of the arrangement of the micropores can be increased. Moreover, when performing a process (3) and a process (4) repeatedly 2 times or more, the starting point of the anodizing process in the process (3) implemented next can be left.

It is preferable to repeat the step (3) and the step (4) twice because the regularity of the pore arrangement is high, more preferably 3 times or more, and more preferably 4 times or more. Is more preferable.
When the above steps are repeated twice or more, the conditions of each step (3) and step (4) may be the same or different. From the viewpoint of improving the degree of ordering, the step (3) is preferably performed by changing the voltage every time. In this case, it is more preferable to gradually change to a high voltage condition from the viewpoint of improving the degree of ordering.

In the state shown in FIG. 2D, the average pore density is preferably 50-1500 / μm ² , and the area ratio occupied by the micropores is preferably 20-50%.

  FIG. 3 is a partial cross-sectional view showing a state after the anodizing treatment (A). As shown in FIG. 3, an anodic oxide film 14 having micropores 16 is formed on the surface of the aluminum substrate 12.

[Heat treatment (B)]
The heat treatment (B) is a treatment in which the anodized film formed by the anodizing treatment (A) is heated at a temperature of 50 ° C. or higher for at least 10 minutes.
In order to perform this heat treatment (B), the aluminum substrate on which the anodized film is formed may be heated under the above conditions.
As a result of intensive studies, the present inventors have found that the electrolytic solution used in the anodizing treatment, the alumina solution used in the film removal treatment, and the treatment used for the removal of the aluminum substrate and the micropore penetration treatment described later. The fact that acid ions derived from the liquid (for example, SO ₄ ^2- when sulfuric acid is used as the electrolyte) remains in the anodized film deteriorates the acid resistance and alkali resistance of the anodized film. I found it.
By heating the anodized film, the acid ions remaining in the anodized film are removed, and the acid resistance and alkali resistance of the anodized film are improved. The acid ions remaining in the anodic oxide film are dissolved in the water remaining in the anodic oxide film, and when the anodic oxide film is heated, the acid ions are evaporated together with the evaporation of the water remaining in the anodic oxide film. Is thought to be removed.

When the heating temperature is less than 50 ° C., the effect of removing the acid ions remaining in the anodized film cannot be sufficiently exhibited.
The heating temperature is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, and still more preferably 400 ° C. or higher.
However, if the heating temperature is too high, the aluminum substrate on which the anodized film is formed may be deformed by heat. Therefore, the heating temperature is preferably 800 ° C. or lower.

When the heating time is less than 10 minutes, the effect of removing the acid ions remaining in the anodized film cannot be sufficiently exhibited.
The heating time is preferably 15 minutes or longer, more preferably 30 minutes or longer, still more preferably 1 hour or longer.
Heating for 10 hours or longer no longer contributes to the action of removing the acid ions remaining in the anodized film, which is not preferable from the viewpoint of yield and energy efficiency. Although depending on the heating temperature, when heated for 15 hours or longer, the aluminum substrate on which the anodized film is formed may be deformed by heat.

  The anodized film after heating is preferably cooled rapidly.

[Separation (C)]
In the separation treatment (C), when the anodizing treatment (A) or the heating treatment (B) is performed, the aluminum substrate is removed after the heating treatment (B), and the oxide film is separated from the aluminum substrate.
The aluminum substrate is removed by dissolving the aluminum substrate 12 from the state shown in FIG. FIG. 4 is a partial cross-sectional view showing a state after the separation process (C), and shows a fine structure made of the anodic oxide film 14 having the micropores 16.
Therefore, in the aluminum removal treatment, a treatment solution that does not dissolve alumina but dissolves aluminum is used.

The treatment liquid is not particularly limited as long as it does not dissolve alumina and dissolves aluminum. For example, an aqueous solution such as mercury chloride, bromine / methanol mixture, bromine / ethanol mixture, aqua regia, hydrochloric acid / copper chloride mixture, etc. Etc.
As a density | concentration, 0.01-10 mol / L is preferable and 0.05-5 mol / L is more preferable.
As processing temperature, -10 degreeC-80 degreeC are preferable, and 0 degreeC-60 degreeC is preferable.

  The aluminum removal treatment is performed by contacting with the treatment liquid described above. The method of making it contact is not specifically limited, For example, the immersion method and the spray method are mentioned. Of these, the dipping method is preferred. The contact time at this time is preferably 10 seconds to 5 hours, and more preferably 1 minute to 3 hours.

  The film thickness of the anodized film after the aluminum removal treatment is preferably 1 to 1000 μm, and more preferably 10 to 500 μm.

  After the aluminum removal treatment, the anodized film 14 is preferably washed with water before the penetration treatment (D) described later. In order to suppress changes in the pore diameter of the micropores 16 due to hydration, the water washing treatment is preferably performed at 30 ° C. or lower.

[Penetration treatment (D)]
The penetration treatment (D) is a treatment for penetrating the micropores of the oxide film separated by the separation treatment (C).
In the penetrating treatment (D), the anodic oxide film 14 having the micropores 16 shown in FIG. 4 is immersed in an acid aqueous solution or an alkali aqueous solution to partially dissolve the anodic oxide film 14. Thereby, the anodic oxide film 14 at the bottom of the micropore 16 is removed, and the micropore 16 penetrates (a micropore through hole 18 is formed). FIG. 5 is a partial cross-sectional perspective view showing a state after the penetration treatment (C), and shows a fine structure made of the anodic oxide film 14 having the micropore through holes 18.
In FIG. 5, all the micropores existing in the anodic oxide film 14 are micropore through holes 18, but all the micropores existing in the anodic oxide film do not pass through by the penetration treatment (D). Also good. However, it is preferable that 70% of the micropores existing in the anodized film penetrate through the penetration treatment (D).

When an aqueous acid solution is used for the penetration treatment (D), it is preferable to use an aqueous solution of an inorganic acid such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, or a mixture thereof. The concentration of the acid aqueous solution is preferably 1 to 10% by mass. The temperature of the acid aqueous solution is preferably 25 to 40 ° C.
When an alkaline aqueous solution is used for the penetration treatment (D), it is preferable to use an aqueous solution of at least one alkali selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide. The concentration of the alkaline aqueous solution is preferably 0.1 to 5% by mass. The temperature of the alkaline aqueous solution is preferably 20 to 35 ° C.
Specifically, for example, 50 g / L, 40 ° C. phosphoric acid aqueous solution, 0.5 g / L, 30 ° C. sodium hydroxide aqueous solution or 0.5 g / L, 30 ° C. potassium hydroxide aqueous solution is preferably used. .
The immersion time in the acid aqueous solution or alkali aqueous solution is preferably 8 to 120 minutes, more preferably 10 to 90 minutes, and still more preferably 15 to 60 minutes.

  The film thickness of the anodized film after the penetration treatment (D) is preferably 1 to 1000 μm, and more preferably 10 to 500 μm.

  After the penetration treatment (D), the anodized film 14 is washed with water. In order to suppress a change in the pore diameter of the micropore through hole 18 due to hydration, the water washing treatment is preferably performed at 30 ° C. or lower.

[Protection treatment (E)]
The protective treatment (E) is a treatment for forming a protective film that prevents hydration on the surface of the oxide film after the penetration treatment (D).
In the protection treatment (E), over the entire surface of the anodic oxide film 14 including the inside of the micropore through-hole 18 with respect to the porous alumina membrane filter including the anodic oxide film 14 having the micropore through-hole 18 shown in FIG. Then, a protective film that prevents hydration of the anodized film is formed.

  Examples of the protective film include an inorganic protective film containing at least one selected from the group consisting of Zr element and Si element, or an organic protective film containing a water-insoluble polymer.

<Inorganic protective film>
The formation of the protective film containing the Zr element is not particularly limited, but, for example, a method in which the protective film is directly immersed in an aqueous solution in which a zirconium compound is dissolved is generally used. From the viewpoint of the robustness / stability of the protective film It is preferable to use an aqueous solution in which a phosphorus compound is dissolved together.

  Zirconium compounds include zirconium, fluoride fluoride, sodium fluoride zirconate, calcium fluoride zirconate, zirconium fluoride, zirconium chloride, zirconium oxychloride, zirconium oxynitrate, zirconium sulfate, zirconium ethoxide, zirconium propoxide, zirconium Butoxide, zirconium acetylacetonate, tetrachlorobis (tetrahydrofuran) zirconium, bis (methylcyclopentadienyl) zirconium dichloride, dicyclopentadienylzirconium dichloride, ethylenebis (indenyl) zirconium (IV) dichloride, etc. can be used. Sodium fluorinated zirconate is preferred. Moreover, as a density | concentration, 0.01-10 wt% is preferable from a viewpoint of the uniformity of a protective film thickness, and 0.05-5 wt% is more preferable.

  As the phosphorus compound, phosphoric acid, sodium phosphate, calcium phosphate, sodium hydrogen phosphate, calcium hydrogen phosphate and the like can be used, and sodium hydrogen phosphate is particularly preferable. Moreover, as a density | concentration, 0.1-20 wt% is preferable from a viewpoint of the uniformity of a protective film thickness, and 0.5-10 wt% is more preferable.

Moreover, since the function which prevents the hydration of the anodic oxide film of the protective film formed improves, it is preferable to include tannic acid in the aqueous solution in which the zirconium compound is dissolved in the immersion treatment. In this case, the concentration of tannic acid in the aqueous solution is preferably 0.05 to 10 wt%, and more preferably 0.1 to 5 wt%.
Moreover, as processing temperature, 0-120 degreeC is preferable and 20-100 degreeC is more preferable.

The formation of the protective film containing Si element is not particularly limited, but, for example, a method in which the protective film is directly immersed in an aqueous solution in which an alkali metal silicate is dissolved is generally used.
The aqueous solution of the alkali metal silicate is composed of a ratio of silicon oxide SiO ₂ and alkali metal oxide M ₂ O (generally expressed as a molar ratio of [SiO ₂ ] / [M ₂ O]) and concentration. It is possible to adjust the protective film thickness. Here, as M, sodium and potassium are particularly preferably used.
As a molar ratio, [SiO ₂ ] / [M ₂ O] is preferably 0.1 to 5.0, and more preferably 0.5 to 3.0. The content of SiO _2, preferably from 0.1 to 20 mass%, 0.5 to 10 mass% is more preferable.

<Organic protective film>
As the organic protective film, a method in which only the solvent is volatilized by heat treatment after being directly immersed in an organic solvent in which a water-insoluble polymer is dissolved is preferable.

Examples of the water-insoluble polymer include polyvinylidene chloride, poly (meth) acrylonitrile, polysulfone, polyvinyl chloride, polyethylene, polycarbonate, polystyrene, polyamide, cellophane and the like.
Examples of organic solvents include ethylene dichloride, cyclohexanone, methyl ethyl ketone, methanol, ethanol, propanol, ethylene glycol monomethyl ether, 1-methoxy-2-propanol, 2-methoxyethyl acetate, 1-methoxy-2-propyl acetate, dimethoxyethane. , Methyl lactate, ethyl lactate, N, N-dimethylacetamide, N, N-dimethylformamide, tetramethylurea, N-methylpyrrolidone, dimethyl sulfoxide, sulfolane, γ-butyrolactone, toluene, and the like. As a density | concentration, 0.1-50 wt% is preferable and 1-30 wt% is more preferable.
Moreover, as heating temperature at the time of solvent volatilization, 30-300 degreeC is preferable and 50-200 degreeC is more preferable.

  After the protective film formation treatment, the thickness of the protective film is preferably 1 to 50 nm, and more preferably 5 to 25 nm.

[Perforated material]
The pore material constituting the precision filter unit of the present invention has an average pore diameter of 500 nm to 10 mm, a pore ratio higher than that of the porous alumina membrane filter, and a Young's modulus larger than 660 MPa. Material.

ここで、Ｙｉは、４９ｍｍ²（７ｍｍ×７ｍｍ）の範囲で測定された１個の孔の等価円直径である。 Here, the shape of the “hole” of the hole material is not particularly limited, and may be, for example, a circular hole or a mesh (mesh) hole.
Therefore, the “average pore diameter” in the above-mentioned porous material is a value obtained by taking the surface photograph with an optical microscope and obtaining the hole existing in the visual field of 7 mm × 7 mm by the following formula.

Here, Yi is an equivalent circular diameter of one hole measured in a range of 49 mm ² (7 mm × 7 mm).

  In the present invention, the average pore diameter is 500 nm to 10 mm, preferably 750 nm to 5 mm, and more preferably 1 μm to 1 mm. When the average pore diameter is in this range, the pressure resistance of the precision filter unit of the present invention used with the porous alumina membrane filter is excellent and the filtration flow rate is also improved.

  Further, the pore material has a higher porosity than that of the porous alumina membrane filter. This means that the pore material does not interfere with the filtration performance of the porous alumina membrane filter. Is clearly defined.

  Moreover, the Young's modulus of the porous material is larger than 660 MPa, preferably 800 MPa to 500 GPa, and more preferably 1 GPa to 1000 GPa.

In the present invention, the material is not particularly limited to such a porous material, but is preferably made of Teflon (registered trademark, the same shall apply hereinafter), stainless steel, nylon or the like.
Specifically, for example, “Teflon mesh dish (pore diameter: 5 mm, dish outer diameter: 47 mm, opening ratio: 82%, Young's modulus: 800 MPa” manufactured by Endo Kagaku Co., Ltd. ) ”,“ Stainless steel filter support (pore diameter: 0.1 mm, outer diameter of dish: 47 mm, opening ratio: 78%, Young's modulus: 26000 MPa) ”manufactured by Millipore,“ Nylon mesh (pore diameter: 20 μm, Dish outer diameter: 47 mm, opening ratio: 75%, Young's modulus: 7600 MPa ”,“ Nylon mesh (pore diameter: 1 μm, dish outer diameter: 47 mm, opening ratio: 68%, Young's modulus: 7600 MPa) ”manufactured by Semitech Can be used.

The precision filter unit of the present invention is such that the porous material is provided in contact with at least one surface of the porous alumina membrane filter, and is provided in contact with both surfaces. preferable. In addition, when the said porous material touches only the surface of the one side of the said porous alumina membrane filter, it is preferable to be provided so that the lower surface of the said porous alumina membrane filter may be touched.
By providing the porous material so as to be in contact with the surface of the porous alumina membrane filter, the obtained precision filter unit of the present invention is excellent in pressure resistance and the filtration flow rate is also improved. This is because the high pressure of the anodic oxide film that forms the porous alumina membrane filter distributes the pressure during filtration uniformly, and the pore material serves as a cushion, resulting in good bending strength. This is thought to be because of

  The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these.

Example 1
1. Production of porous alumina membrane filter (1) Electropolishing treatment After cutting a high-purity aluminum substrate (manufactured by Sumitomo Light Metal Co., Ltd., purity 99.99 mass%, thickness 0.4 mm) so that it can be anodized with a diameter of 47 mmΦ. Then, an electrolytic polishing treatment was performed using an electropolishing liquid having the following composition under the conditions of a voltage of 25 V, a liquid temperature of 65 ° C., and a liquid flow rate of 3.0 m / min.
The cathode was a carbon electrode, and GP0110-30R (manufactured by Takasago Seisakusho) was used as the power source. The flow rate of the electrolytic solution was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE).

<Electrolytic polishing liquid composition>
-660 mL of 85% by mass phosphoric acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.)
・ Pure water 160mL
・ Sulfuric acid 150mL
・ Ethylene glycol 30mL

(2) Anodizing treatment The electropolished sample obtained above was subjected to 0.30 mol / L sulfuric acid electrolytic solution for 1 hour under conditions of a voltage of 25 V, a liquid temperature of 15 ° C., and a liquid flow rate of 3.0 m / min. Anodized. Further, the anodized sample was immersed in a mixed solution of 0.5 mol / L phosphoric acid at 40 ° C. for 20 minutes for film removal treatment.
After these treatments were repeated four times in this order, re-anodization treatment was performed for 5 hours with an electrolyte of 0.30 mol / L sulfuric acid under conditions of a voltage of 25 V, a liquid temperature of 15 ° C., and a liquid flow rate of 3.0 m / min. Further, the micropores 16 are formed in a straight tubular and honeycomb shape on the surface of the aluminum substrate 12 by performing a film removal treatment by dipping for 20 minutes at 40 ° C. using a mixed aqueous solution of 0.5 mol / L phosphoric acid. Arranged anodic oxide films 14 were formed (see FIG. 2D and FIG. 3).

  In both the anodic oxidation treatment and the re-anodic oxidation treatment, the cathode was a stainless electrode, and the power supply was GP0110-30R (manufactured by Takasago Seisakusho). In addition, NeoCool BD36 (manufactured by Yamato Kagaku Co.) was used as the cooling device, and Pear Stirrer PS-100 (manufactured by EYELA) was used as the stirring and heating device. The flow rate of the electrolyte was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE).

(3) Separation treatment The sample after the anodizing treatment obtained above is immersed in a mixed aqueous solution of 20% by mass hydrochloric acid and 0.1 mol / L cupric chloride at 25 ° C. for 20 minutes. Then, the aluminum substrate 12 was dissolved and removed, and a fine structure made of the anodized film 14 having the micropores 16 was produced (see FIG. 4).

(4) Penetration treatment After the fine structure obtained above was immersed in a 0.10 mol / L potassium chloride aqueous solution at 25 ° C. for 2 minutes, 0.10 mol / L was formed on the surface to penetrate the micropores. By contacting potassium hydroxide at 20 ° C. for 10 minutes, a microstructure comprising the anodic oxide film 12 having the micropore through-holes 16 was produced (see FIG. 5).

2. Shape analysis of porous alumina membrane filter A surface photograph (magnification 20000 times) was taken with FE-SEM, and the average pore diameter and standard deviation of the pore diameter were calculated by the following formula for the micropores present in the 1 μm × 1 μm visual field. The aperture ratio was calculated. As a result, the average pore diameter was 38 nm, the standard deviation was 2.4 nm, and the aperture ratio was 45%.

Similarly, the degree of ordering defined by the following formula (1) was determined using 300 arbitrary micropores. As a result, the degree of ordering was 90%.
Ordering degree (%) = B / A × 100 (1)
In the above formula (1), A represents the total number of micropores in the measurement range. B is centered on the center of gravity of one micropore, and when a circle with the shortest radius inscribed in the edge of another micropore is drawn, the center of gravity of the micropore other than the one micropore is placed inside the circle. This represents the number in the measurement range of the one micropore to be included.

3. Production of precision filter unit On one surface of the porous alumina membrane filter obtained above, “Teflon mesh dish made by Endo Kagaku (pore diameter: 5 mm / outer diameter: 47 mm / opening ratio: 82% / Young's modulus: 800 MPa) Was grounded, and the precision filter unit of Example 1 was obtained.

(Example 2)
A precision filter unit of Example 2 was obtained in the same manner as in Example 1 except that the porous material was grounded on both surfaces of the porous alumina membrane filter.

(Example 3)
Except that the porous material was used instead of Millipore's “stainless steel filter support (pore diameter: 0.1 mm / outside diameter of the dish: 47 mm / opening ratio: 78% / Young's modulus: 26000 MPa)”, the same as in Example 1 The precision filter unit of Example 3 was obtained by the method.

Example 4
Except that the porous material was used instead of “Nylon mesh (pore diameter: 20 μm / outside diameter of the dish: 47 mm / opening ratio: 75% / Young's modulus: 7600 MPa)” manufactured by Semitec Corporation, the same method as in Example 1, A precision filter unit of Example 4 was obtained.

(Example 5)
The same procedure as in Example 1 was performed except that the porous material was used instead of “Nylon mesh (pore diameter: 1 μm / outer diameter: 47 mm / opening ratio: 68% / Young's modulus: 7600 MPa)” manufactured by Semitec. The precision filter unit of Example 5 was obtained.

(Example 6)
The precision filter unit of Example 6 was obtained in the same manner as in Example 1 except that the electrolytic solution used in the anodizing treatment was 0.50 mol / L oxalic acid electrolytic solution and the voltage was 40V.
As in Example 1, the average pore size of the micropores, the standard deviation of the pore size, the aperture ratio, and the degree of ordering were evaluated. The average pore size: 69 nm, the standard deviation: 2.9 nm, the aperture ratio: 53%, the ordering The degree was 90%.

(Comparative Example 1)
The porous alumina membrane filter produced in Example 1 was used without using a porous material.

(Comparative Example 2)
A precision filter unit of Comparative Example 2 was obtained in the same manner as in Example 1, except that the electrolytic solution used in the anodizing treatment was 0.50 mol / L phosphoric acid.
As in Example 1, the average pore size of the micropore, the standard deviation of the pore size, the aperture ratio, and the degree of ordering were evaluated. The average pore size: 41 nm, the standard deviation: 11.8 nm, the aperture ratio: 46%, the degree of ordering 13%.

<Pressure resistance evaluation of filter unit>
In order to evaluate the pressure resistance of the precision filter unit obtained above (for the first comparative example, a porous alumina membrane filter), ultrapure water was added at 0.2 MPa to 10 MPa using a “stainless steel filter cartridge” manufactured by Millipore. The treatment was performed for 1 minute under the condition that the amount of pressurization was increased every 0.2 MPa up to 0 MPa.
The treated porous alumina membrane filter was observed for damage, and the upper limit of the amount of pressure at which damage did not occur was described. Larger values indicate better pressure resistance. The results are shown in Table 1.

  As shown in Table 1, a porous alumina membrane filter in which the degree of ordering and the standard deviation of the pore diameter are in a predetermined range, and the porosity is high with respect to the porous alumina membrane filter, and the average pore diameter and Young's modulus are predetermined. It was found that the pressure resistance of the porous alumina membrane filter was dramatically improved by using a porous material in the range.

FIG. 1 is an explanatory diagram of a method for calculating the degree of ordering of pores. FIG. 2 is a schematic end view of an aluminum substrate and an anodized film formed on the aluminum substrate for explaining the porous alumina membrane filter used in the present invention. FIG. 3 is a partial cross-sectional view showing a state after the anodizing treatment (A). FIG. 4 is a partial cross-sectional view showing a state after the separation process (C). FIG. 5 is a partial cross-sectional view showing a state after the penetration process (D).

Explanation of symbols

1, 2, 4, 5, 7, 8 Micropore 3, 6, 9 Circle 12, 12a, 12b, Aluminum substrate 14, 14a, 14b, 14c, 14d Anodized film 16, 16a, 16b, 16c, 16d Micropore 18: Micropore through hole 20 Deformed portion 30 Inflection point

Claims (5)

A porous alumina membrane filter comprising an anodized film of aluminum, having a micropore whose degree of ordering defined by the following formula (1) is 50% or more and whose standard deviation of pore diameter is within 10% of the average pore diameter When,
A porous material in contact with the surface of at least one side of the porous alumina membrane filter, having an average pore diameter of 500 nm to 10 mm, and an opening area per unit area is larger than an opening area per unit area of the porous alumina membrane filter And a porous material having a Young's modulus larger than 660 MPa,
A precision filter unit comprising at least
Ordering degree (%) = B / A × 100 (1)
In the formula (1), A represents the total number of micropores in the measurement range. B is centered on the center of gravity of one micropore, and when a circle with the shortest radius inscribed in the edge of another micropore is drawn, the center of gravity of the micropore other than the one micropore is placed inside the circle. This represents the number in the measurement range of the one micropore to be included.   The precision filter unit according to claim 1, wherein the porous material is in contact with surfaces on both sides of the porous alumina membrane filter. The porous alumina membrane filter is at least,
Anodizing to form an oxide film having micropores by anodizing an aluminum substrate;
A separation treatment for removing the aluminum substrate after the anodizing treatment and separating the oxide film from the aluminum substrate;
A penetration treatment for penetrating the micropores of the oxide film separated by the separation treatment;
The precision filter unit according to claim 1, which is formed by applying the components in this order.   The precision filter unit according to claim 3, wherein a heat treatment is performed to heat the oxide film formed by the anodization treatment at a temperature of 50 ° C. or higher for at least 10 minutes before the separation treatment.   5. The precision filter unit according to claim 3, wherein after the penetration treatment, a protective treatment for forming a protective film that prevents hydration is applied to the surface of the oxide film.

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